1. Field of the Invention
The present invention relates to a honeycomb structure.
2. Discussion of the Background
Exhaust gas discharged from internal combustion engines, such as diesel engines, contains particulate matter (hereinafter, also referred to as “PM”). The PM has harmful effects on the environment and the human bodies, and thus the PM has been a recent issue.
In order to capture PM in exhaust gas to purify the exhaust gas, various honeycomb filters have been proposed as filters. These honeycomb filters each include a honeycomb structure made of a material such as cordierite, silicon carbide, or aluminum titanate.
A honeycomb structure including aluminum titanate has a melting temperature higher than that of a honeycomb structure including cordierite. It is therefore known that the honeycomb structure including aluminum titanate is less likely to be damaged by melting upon burning PM in the case where the honeycomb structure is used as a honeycomb filter. In addition, the honeycomb structure including aluminum titanate has a coefficient of thermal expansion lower than that of a honeycomb structure including silicon carbide. It is therefore known that the honeycomb structure including aluminum titanate is less likely to be damaged by heat applied upon burning PM even in the case where the honeycomb structure is used as a large-size filter.
Since aluminum titanate has anisotropy in crystallographic axes, fine cracks occur in the honeycomb structure including aluminum titanate. Thus, disadvantageously, it is considered that the honeycomb structure including aluminum titanate is made to have a low breaking strength and is likely to be decomposed by heat.
US 2006/0021309A discloses a honeycomb filter which includes a honeycomb structure mainly including aluminum titanate and showing small variation in the pore diameter distribution. The honeycomb structure is manufactured as follows: a material mixture mainly composed of Al2O3 and TiO2 is prepared; an oxide of a substance such as Bi, Ca, or Y is added to the material mixture; and the resulting mixture is fired.
The contents of US2006/0021309A are incorporated herein by reference in their entirety.